The present invention relates to new cytotoxic tris(oxazole)-containing macrolides obtained by chemical modification of marine natural products.
Marine organisms, especially soft corals, sponges and tunicates, provide many secondary metabolites and exhibit a varying degree of biological activity (Reference 1). An important family of these metabolites is the cytotoxic tris(oxazole)-containing macrolide family; in 1986 it was reported the structure of the three first tris(oxazole)-containing macrolides: Ulapualide A and B (Reference 2) and Kabiramide C (Reference 3). 
Since then, over 30 additional tris(oxazole)containing macrolides have been published (Reference 4).
The present invention relates to now cytotoxic tris(oxazole)-containing macrolides having the formula (I): 
wherein X represents a lower alkyl; R1 and R2 represent hydrogen or lower alkyl; R3a represents hydrogen, and R3b represents 
or R3a and R3b together represent oxygen; R4 represents hydrogen, lower alkoxy or lower alkyl; R5 represents hydrogen, carbarnoyl, or lower alkanoyl; R6a represents hydrogen, and R6b represents hydroxy, or R6a and R6b together represent oxygen; R7 represents hydrogen, lower alkyl, or hydroxymethyl; R8 represents lower alkoxy or lower alkyl; Y1 represents hydrogen or methyl, and y2 represents hydrogen, or Y1 and Y2 together represent a double bond.